In third generation (3G) wireless communication systems, a wireless transmit/receive unit (WTRU) has the ability to support multiple applications with different quality of services (QoS) requirements running simultaneously. Applications associated with individual data flows from a radio link control layer (RLC) are known as logical channels. These logical channels are mapped to transport channels (TrCH) within the medium access control (MAC) layer. Each TrCH is associated with a specific QoS. Logical channels with similar QoS requirements are mapped to common TrCHs.
Several TrCHs can be multiplexed into a coded composite transport channel (CCTrCH). Each TrCH has a specified coding rate and rate matching attributes within the CCTrCH to allow for different levels of error protection. Combination of TrCHs that are allowed in a CCTrCH transmit time interval (TTI) are defined by a transport format combination set (TFCS). The TFCS defines the allowed multiplexing combinations of TrCHs within each CCTrCH TTI.
Each TTI, the MAC selects a transport format combination (TFC) from the TFCS or a configured TFC subset. TFCs are selected based on the transmission priority of the logical channels that are mapped to each TrCH. TFC selection rules are based on maximizing transmission of the highest priority data.
The TFCS is configured to allow certain TrCH data combinations and not allow others. This mechanism is used to ensure maximum and minimum data rates of each TrCH within the CCTrCH.
Each TTI, TFCs within the TFCS are checked to determine if the TFCs can be supported by the available transmission power of the WTRU. A TFC which can not be supported is considered to be in an excess power state and can be transmitted for a short period. If the transmission power requirement is not satisfied within this period the TFC is blocked from transmission. Certain TFCs in a “minimum set” are excluded from being blocked. These transport channel configurations for the TFCS, TFC selection rules and the minimum set are used to maintain QoS of individual data flows.
Enhanced uplink (EU) has been developed to reduce transmission latency and increase radio resource efficiency in the uplink. A WTRU is provided with only one EU TrCH. Since there is only one EU TrCH per WTRU, just a list of transport formats (TFs) for the EU TrCH exists that does not distinguish requirements for different logical channel priorities and QoS. The configured CCTrCH TFCS and TFC selection rules to properly coordinate transmission multiplexing within TTIs only work where multiple TrCHs are provided and logical channels of common QoS requirements are mapped to specific TrCHs. Since there is only one EU TrCH, these multiplexing rules and the QoS provided for individual data flows are not available for EU.
In order to properly maintain QoS requirements of individual data flows, it is necessary to define new WTRU multiplexing rules for logical channels or MAC-d flows mapped onto enhanced uplink medium access control (MAC-e) protocol data units (PDUs).